TY  - JOUR
A1  - Wegener, Michael
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Dansachmüller, M.
A1  - Schwödiauer, R.
A1  - Bauer-Gogonea, Simona
A1  - Bauer, Siegfried
A1  - Paajanen, Mika
A1  - Minkkinen, Hannu
A1  - Raukola, J.
T1  - Controlled inflation of voids in cellular polymer ferroelectrets : optimizing electromechanical transducer properties
N2  - When exposed to sufficiently high electric fields, polymer-foam electret materials with closed cells exhibit ferroelectric-like behavior and may therefore be called ferroelectrets. In cellular ferroelectrets, the influence of the cell size and shape distributions on the application-relevant properties is not yet understood. Therefore, controlled inflation experiments were carried out on cellular polypropylene films, and the resulting elastical and electromechanical parameters were determined. The elastic modulus in the thickness direction shows a minimum with a corresponding maximum in the electromechanical transducer coefficient. The resonance frequency shifts as a function of the elastic modulus and the relative density of the inflated cellular films. Therefore, the transducer properties of cellular ferroelectrets can be optimized by means of controlled inflation. (C) 2004 American Institute of Physics
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Bauer-Gogonea, Simona
A1  - Bauer, Siegfried
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Dielectric investigation of photo-induced chromophore degradation in nonlinear optical side-chain polymer electrets
N2  - Organic materials with non-centrosymmetric chromophores are known to be susceptible to a number of photochemical processes, including reversible isomerization reactions as well as irreversible photo-oxidation or photo- reduction reactions. Reversible isomerization is the basis for a variety of applications, such as photo-induced poling, optical data storage and optical grating formation. The irreversible processes that involve the destruction of the chromophores have been found useful for the fabrication of optical waveguides, but they also limit the life times of polymeric photonic devices. In this paper, it is demonstrated that dielectric measurements allow for an in-depth investigation of non-reversible chromophore degradation processes in a typical side-chain polymer. The time- and temperature-dependent dielectric function of the polymer at 1 kHz enables us to follow the chromophore-degradation kinetics and to monitor the bleaching depth as a function of time at room and elevated temperatures
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Bauer, Siegfried
A1  - Gerhard, Reimund
A1  - Sessler, G. M.
T1  - Ferroelectrets : soft electroactive foams for transducers
Y1  - 2004
ER  -